Hello, Welcome to Just Answer and thanks for your question. Sarcoidosis typically waxes and wanes, and sometimes disappears altogether. We aren't 100% sure what causes it, but it appears to be the body's abnormal immune response to something. It can result in problems in the lungs, skin, and other parts of the body. It really isn't that flour would "cause" it but rather that her body's abnormal immune response to the flour causes it. You can read more about the disease below.
Yes, that would be correct, if a little over-simplified. A mask certainly would not hurt to try and could prevent breathing problems for her. It's similar to avoiding roses if you know you are allergic to them. Many women feel their very best when they are pregnant, so it's difficult to know if it was the lack of flour exposure, a hormonal thing, or just waning of sarcoidosis symptoms in a cycle. The mask is certainly a good idea though. If there is a lot of dust involved, it is a good idea for anyone, whether they have had breathing problems or not. It's a medical fact that tiny particles of anything we breathe (regardless of how innocuous) can cause irritation of the air passages.